Chinese state broadcaster CCTV said the six days of drills feature simulated anti-aircraft, anti-submarine and search-and-rescue operations, including electronic countermeasures and other sensitive technologies.

Retired major general Yin Zhuo said it shows a high degree of trust between the sides.

"It's an excellent exchange for China to be able to drill jointly in such sensitive areas," Yin told CCTV.

China's Defense Ministry said China was sending two submarines and 16 ships to take part, including destroyers, escort vessels and hospital ships. The deputy chiefs of the countries' navies oversaw the start of drills in the northeastern Chinese port of Qingdao, the home of China's northern fleet.

The two militaries hold frequent exchanges, despite recent disputes over Chinese copying of Russian military technology such as Sukhoi jet fighters. China was a key customer for the former Soviet arms industry, but recent technological advances at home have made it far less dependent on Russian weaponry.

Much of that cooperation takes place within the confines of the Shanghai Cooperation Organization, a grouping of Central Asian states that seeks to check U.S. influence in the region and began holding joint drills in 2005.

Formerly Cold War rivals for leadership of the communist world, China and Russia have since found common ground in countering liberal democratizing trends across Asia and Eastern Europe and frequently vote against Western initiatives in the United Nations Security Council.

Most recently, they have united to block any U.N. actions on Syrian violence that could lead to some form of humanitarian intervention, a prospect both nations abhor.